Induction heating of rail welds

ABSTRACT

An apparatus ( 10 ) and method for preheating welds uses a centered induction plate ( 12 ) having preferably a plurality of induction coils ( 30, 32 ) to impart the generation of heat in the materials to be welded ( 14 ), being interactively controlled by at least a temperature sensor ( 90, 92 ) and power supply control loop ( 16 ) so that even preheating can be obtained for a selected length of time given the parameters of the weld desired.

CLAIM OF PRIORITY

Priority is claimed based upon Provisional Patent Application Ser. No.60/209,030, filed Jun. 2, 2000, which is incorporated by reference as iffully set forth herein.

STATEMENT OF INVENTORSHIP

Assignee, Holland Company, believes that the subject matter was theinvention of Richard F. Miller.

FIELD OF THE INVENTION

Some welding techniques require precise consistent and controlledheating, which is difficult or impossible to obtain with torches, gasburners or other electric devices. Instead, this is achievable throughthe use of induction heating wherein a plate or other locating andholding device is placed in a gap between work pieces to be welded, theplate containing an array of induction heating elements which, whenenergized, produce shaped, varying electromagnetic fields which linkwith and induce a voltage in the work pieces which in turn results ineddy current flows and subsequent power losses, as well as hysteresislosses, so that the workpiece temperature is raised to a desired,uniform level prior to welding.

BACKGROUND OF THE INVENTION

1. Summary of Invention

The preferred embodiment is adapted to use in welding railroad rails,however, other difficult to weld work pieces could be advantageouslypreheated with the invention. The descriptions herein of rail weldsshould be considered with this more expansive use in mind.

Induction type heat allows for precise heating at ideal locations andcan be used to control heat gradients. This control is possible thoughuse of a feedback system, controller, coil arrangement and a positioningmechanism. This eliminates the human element, resulting in an automatedhigh quality weld preheat method.

The use of an automated electrically powered and computer controlledinduction heating system using the induction heating coils and heatingplate with sensitive temperature control and feedback interfaced withinthe power supply enables higher quality and more consistent welds ofdifficult to weld pieces such as railroad rails and similar highstrength and complex shaped generally ferric items. One advantage inthis regard is the ability to manipulate the heat gradient. Alsoincluded in advantages over prior art methods are the facts that noconsumables are required, there is no need for gases or fuel on board orduring transportation and cleanliness—in that there are no combustionbyproducts. The invention provides consistent heat through a wide rangeof ambient temperatures. Another advantage is that of use in differentrail geometry, rail chemistries and welding methods. In addition toheating, an analogous plate or array can be used to control coolingafter welding.

In the preferred and alternative embodiments, the invention envisionsthe use of independent, single or multiple coils and/or power units.Independent, single or multiple coils and/or power units enable theprecise location of heating, subdivides locations of heating andprovides flexibility in the control of heating areas. An added benefitof using an independent preheating unit, as compared to including thewelder or portions of the welder's power supply or the like is that ofefficiencies gains due to multi tasking during welding process. Whilepreheating is occurring, the welder itself can be independently set upfor welding operations, or, indeed, one rail may be welded while theadjacent rail is preheated, should the rail gaps be proximate the railwelder's cable runs.

2. Description of Related Art

While preheating of metal pieces for welding as a general concept iswell known, heretofore generally manual application of heat has beenused. The use of items such as gas or other torches, gas burners orelectrically powered devices. Field welding in the past commonlypreheated with torches and gas burners. Such methods introduce humanintervention positioning, timing or estimating heat input andtemperature. Combustion variables including fuel, air, pressure,position and shape of a flame relative to rails, ignition steps, initialtemperature of the workpieces and even weather contribute to imprecisionin temperature control in the prior art. Resistance electrical deviceshave power and conductivity variables including both electrical andthermal limitations that also contribute to imprecision in temperaturecontrol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the layout of the components of theinvention.

FIG. 2 is an elevational view showing the induction plate of theinvention.

FIG. 2A is an elevational view showing an induction coil with ferritecore.

FIG. 3 is a wiring diagram showing the control wiring of the invention.

FIG. 4 is a wiring diagram showing the power supply wiring to controlseparate heating zones.

FIG. 5 is a side elevational view showing the induction plate of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Weld quality and consistency can be improved with precise control ofheating (temperatures, location zones and heat gradients). Heatingbecomes more critical when dealing with certain alloying, geometry orambient temperatures. This is more of an art gained through experienceor a routine that must be followed carefully to attempt to produceconsistent, quality welds.

An induction heating system 10 uses a tool or plate 12 to heat arailroad rail 14. Power control 16 is operatively connected to a pair ofpower supplies 18,20. Power supplies 18,20 are in turn operativelyconnected to a heat zone control unit 22 using control outputconnections 24, 26. Cables (not shown) interconnect power supplies 18,20to plate 12, generally, and to heating elements 30, 32 specificallythrough connectors 34, 36. FIG. 2A shows the heating element 32 in moredetail. Each element 30, 32 is generally broken out into a separateheating module 38, 40 using the elements 30, 32 and other features morefully described below to provide a unitary heating module 38, 40. Theheating system 10 is a 5 Kw, 25 Khz induction heating system broken outin the form of two 2.5 Kw modules 38, 40. While this is the preferredcapacity of the system, different welding operations couldadvantageously be accommodated through the use of a heating system witha different heating capacity. These are capable of independent heatingof two heat zones, 42, 44. Each module 38, 40 is connected to a heatingelement 30, 32 with ferrite cores 46, 48 in a common housing in plate 12capable of being inserted in an approximate one inch gap between rails14. It will be understood that the rails 14 are shown in section and inthe field there will be to rails 14 with a gap between them intended tobe welded.

For preheating of normal section railroad rails 14 for gas shielded arcwelding, the preferred heat zones 42, 44 consist of two heatinglocations 50, 52 generally near the bottom flanges 54, 56. The preferredembodiment will be further described below after general description ofthe field that requires induction preheating.

Gas shielded arc welding without the preheating taught by the inventionin this application has been practiced under controlled laboratoryand/or workshop conditions but is believed unsuitable for use in thefield. One method used under controlled conditions is generally taughtby U.S. Pat. Nos. 5,773,779 and 5,877,468, which are incorporated byreference as if fully set forth herein. It is believed that one reasonthe method described in these two patents is inoperative in fieldconditions is inadequate control of preheating. Delivery of gas shieldedarc welding equipment and the alignment and restraint of railroad railsand the deployment of a weld containment unit for application of weldbeads is taught in published International Application No. WO 99/31322published 16 Dec. 1998 entitled “Mail Welding Apparatus IncorporatingRail Restraining Device, Weld Containment Device and Weld DeliveryUnit.” The teachings of this application are also incorporated byreference. It is believed that the apparatus and method taught hereinare essential in effective practice of gas shielded arc welding ofrails.

Additionally, other welding methods are believed to be capable ofenhancement through the use of the invention taught here. Other weldmethods, such as thermite, on site foundry and even certain flux-basedarc welding may prove suitable for high strength welds of complex shapeswith adequate and well controlled preheating.

While the preferred embodiment of induction heating for rail weldingusing gas shielded arc welding anticipates using two heating modules 38,40, other uses could use fewer, more or differently arranged heatingmodules. Thus, for certain rail welding or joining methods it may proveadvantageous to heat the entire rail section simultaneously. Theinvention is not limited to rail welding using two heating modules.

Plate 12 is formed to fully support and contain heating elements 30, 32.Accordingly plate 12 has a body portion 60 ending in a protectiveceramic cover 62 which fully covers ferrite cores 46, 48 and thecorresponding conductors of elements 30, 32. Side edges 64, 66 of plate12 are fitted with centering bar assemblies 68, 70. Assemblies 68, 70use centering adjustment mechanism 72 to adjust bars 74, 76 outwardly orinwardly to fit the rail gap. It will be understood that assemblies 68,70 are symmetric and accordingly only one assembly 70 is shown andillustrated in FIG. 5.

Precise cutting of rails in the field is quite difficult, thus there isoften variation in the size of gaps and the orientation of their faces.The adjustable and expandable centering bar assembles enabling side toside and top to bottom centering are important in aligning plate 12 asclose to the center of the gap as practicable to maximize the uniformheating of the rail ends. In this manner the assemblies 68, 70 arealigned for maximum effectiveness and uniformity, being centered betweenfaces that may themselves be non-parallel due to the difficulty ofcutting in the field.

Each heating element 30, 32 is fitted with a respective pair ofwater/power connections 80, 82 illustrated in FIG. 2A. These enable boththe electrical power connection necessary to energize the ferrite core46, 48 and provide conduits for the transmission of cooling fluid todissipate the heat radiantly transmitted from the preheated rails 14 tothe plate 12. Spring clips 84, 86 are used to retain elements 30, 32 inplace in plate 12.

Temperature measuring devices such as spring loaded thermocouples 90, 92are used as an integral part of both plate 12 and heat zone control unit22. Thermocouples 90, 92 are operatively connected to heat zone controlunit 22 which is in turn used to control power supplies 18, 20. Powersupplies 18, 20 receive signals from unit 22 interconnected throughconnections 24, 26 which provide power on or power off control signalsdepending on the heat measured at thermocouples 90, 92. It will beobserved, particularly from FIG. 1 and 2 that thermocouples 90 and 92are positioned proximate ferrite cores 48, thereby providing an accuratetemperature reading from rails 14 which are heated as a result of theenergizing of elements 30, 32 and particularly cores 46, 48. The generalprinciples of induction heating will be recognized, namely the providingof a sufficiently large energy output at elements 30, 32 and cores 46,48 will create heat in adjacent steel rails 14.

In this manner heat zones 42, 44 are interactively controlled so that acontrolled heat results although a variety of factors, whether animprecise gap, power, magnetic fluctuations, unequal temperaturedifferential or even environmental factors such as a crosswind, impactthe actual temperature and heat distribution in the rails. As notedabove while locating heat zones 42, 44 near the rail flanges isadvantageous for gas shielded arc welding other types of welding mayrequire the use of different heat zones such as heating the entire railsection including flanges, web and head, or for the welding of differentshapes such as I-beams and the like. In these other uses andapplications, the number of heat zones and their orientation can becontrolled consistent with the principles of this invention. The use ofone or more coil elements 30, 32 gives flexibility in applying the twopreferred heat zones 46, 48. In other, particularly non-rail weldingapplications, a single heat zone or multiple heat zones could be used. Aplurality of coil elements, two or more, also provide flexibility intemperature differentials that may be required by particularmetallurgical or welding considerations.

The invention enables precision controlling of the heat gradient in thepieces to be welded. The interactive control between elements 30, 32 andthermocouples 90, 92 in zones 42, 44 enables the ability to manipulatethe effects of applied heat to the particular metallurgy of the rails 14and weld material and method used.

Control unit 22 can also be interconnected to corresponding additionalfixtures or controls. The invention contemplates a feedback system thatenables, but is not limited to input from a robot or positioner or acontroller/computer that calculates heat soak/rail temperature forparticular conditions. With this data compared to the induction heatinputs directly supplied by unit 22 and temperature measurement enabledby thermocouples 90, 92, control unit can be modified for particulartime and energy parameters, given known metallurgical and weldingrequirements.

This full feedback system maximizes the quality control of the weldingprocess so that it will be repeatable and monitored. The full feedbacksystem also records actual temperatures and adjusts automatically. Thefill feedback system is further programmable for various materials,conditions and methods. With greater and better data regarding when theweld pieces reach correct temperature(s) in singular and/or multiplezones fully integrated with weld delivery controls, the user is provideda seamless system with no additional mechanisms, components required,such as the prior art burners or torches, and welding materialsrequiring multiple unrelated and uncontrolled steps. Finally, the fullyintegrated system can be manipulated by robot for deployment, movementsduring heating process and retractment.

In operation, the steps of the invention are premised on the step inwhich each heat zone is monitored by a temperature measuring devicewhich checks temperature on one side of the zone. Even heating isachieved on either side of the zone because the inductor is centeredbetween the rails with a mechanical centering device, whichindependently and exactly centers the inductor relative to side one andside two. By so doing each side is brought up to a preferably preheattemperature even though the rails may have a variable gap. It will benoted that the temperature may, of course, vary based on the materialswelded and the method of welding used.

Rail ends are preheated by induction heating for preparation of welding.The ideal temperature and heat gradient is controlled by a feedbacksystem. The feedback system uses temperature-measuring devices likethermocouple's, pyrometers, and other heat sensors with or without acontrolling device. During the pre-heating, different zone(s) of railends can be simultaneously heated independently of each other.Frequency, proximity and number of cycles allow for control of the heatgradient. This is complemented though coil designs in the tool and/orpower inputs. This tool fits between the rail ends in the gap and can bemanipulated by a robotic arm or manually. The gaps between rails areapproximately ¼″ and up. Material and mechanical designs of this toolenhance durability and efficiencies. Process requirements are monitoredand recorded for quality control. Parameter measurements give a go/no gosignal to proceed with welding or intervene with corrections to meetparameters. In addition post-heating enjoys many of the same benefits.The complete system is mobile and portable.

In operation, each zone begins heating simultaneously. Should one zonereach temperature prior to the other the heater output is reduced so asto maintain at temperature until the second zone also achieves requiredtemperature. Only at this time does the controller send a signal to theweld controller indicating that welding can commence.

1. An induction heating system for preheating first and secondworkpieces to be welded together comprising: a tool having first andsecond opposing sides, and disposed in a gap defined by facing ends ofthe workpieces, the tool further including mechanical centeringassemblies disposed adjacent the facing ends of the workpieces, whereinthe mechanical centering assemblies position the tool longitudinallywith respect to the workpieces for proper proximity to the workpieces; afirst induction heating element affixed to the first side of the tooland disposed proximate the first and second workpieces; a first heatingzone defined by a first temperature sensor positioned proximate thefirst workpiece and the first heating element; a second inductionheating element affixed to the second side of the tool and disposedproximate the first and second workpieces; a second heating zone definedby a second temperature sensor positioned proximate the first workpieceand the second heating element; a controller coupled to the first andsecond temperature sensors, the controller activating the first andsecond heating elements independently to achieve a predetermined weldingtemperature in both first and second heating zones.
 2. The inductionheating system of claim 1, further comprising a first power supplycoupled to the first heating element, and a second power supply coupledto the second heating element, wherein both first and second powersupplies are coupled to the controller.
 3. The induction heating systemof claim 1, wherein the first and second induction heating elements areferrite core heating elements.
 4. The induction heating system of claim1, wherein the temperature sensors comprise thermocouple temperaturesensors.
 5. The induction heating system of claim 1, wherein thetemperature sensors comprise pyrometer temperature sensors.
 6. Theinduction heating system of claim 1, wherein the controller provides adiscernible indication when the workpieces have reached thepredetermined welding temperature.
 7. The induction heating system ofclaim 6, wherein the discernible indication is a visual indication. 8.The induction heating system of claim 1, wherein the controller providespositioning information to a positioning robot that adjusts relativeposition of the tool until the predetermined welding temperature isachieved.
 9. The induction heating system of claim 1, wherein coolingfluid is provided proximate each of the heating elements.
 10. Theinduction heating system of claim 9, wherein the controller controlscooling fluid activation.
 11. The induction heating system of claim 1,wherein there are three or more heating elements.
 12. The inductionheating system of claim 1, wherein there are three or more heatingzones.
 13. The induction heating system of claim 1, wherein the firstand second workpieces are railroad rails.
 14. An induction heatingsystem for preheating first and second workpieces to be welded togethercomprising: a tool disposed in a gap defined by facing ends of theworkpieces, the tool further including mechanical centering assembliesdisposed adjacent the facing ends of the work-pieces, wherein themechanical centering assemblies position the tool longitudinally withrespect to the workpieces for proper proximity to the workpieces; aninduction heating element affixed to the tool and disposed proximate thefirst and second workpieces; a heating zone defined by a temperaturesensor positioned proximate the first workpiece and the heating element;a controller coupled to the temperature sensor, the controlleractivating the heating element to achieve a predetermined weldingtemperature in the heating zone.
 15. An induction heating system forpreheating first and second workpieces to be welded together comprising:a tool disposed in a gap defined by facing ends of the workpieces, thetool further including mechanical centering assemblies disposed adjacentthe facing ends of the workpieces, wherein the mechanical centeringassemblies position the tool longitudinally with respect to theworkpieces for proper proximity to the workpieces; a plurality ofinduction heating elements affixed to the tool and disposed proximatethe first and second workpieces; as plurality of heating zones definedby multiple temperature sensors positioned proximate the first workpieceand the heating elements; a controller coupled to the temperaturesensors, the controller activating the heating elements to achieve apredetermined welding temperature in the heating zones.
 16. An inductionheating system for preheating first and second workpieces to be weldedtogether comprising: mounting means having first and second opposingsides, and disposed in a gap defined by facing ends of the workpieces,wherein the mounting means further further includes mechanical centeringassemblies disposed adjacent the facing ends of the workpieces, whereinthe mechanical centering assemblies position the mounting meanslongitudinally with respect to the workpieces for proper proximity tothe workpieces; a first induction heating means affixed to the firstside of the mounting means and disposed proximate the first and secondworkpieces; a first heating zone defined by a first temperature sensingmeans positioned proximate the first workpiece and the first heatingmeans; a second induction heating means affixed to the second side ofthe mounting means and disposed proximate the first and secondworkpieces; a second heating zone defined by a second temperaturesensing means positioned proximate the first workpiece and the secondheating means; a controller means coupled to the first and secondtemperature sensing means, the controller means activating the first andsecond heating means independently to achieve a predetermined weldingtemperature in both first and second heating zones.
 17. The inductionheating system of claim 16, wherein the mounting means comprises a toolhaving first and second opposing sides.
 18. The induction heating systemof claim 16, further comprising a first power supply means coupled tothe first heating means, and a second power supply means coupled to thesecond heating means, wherein both first and second power supplies meansare coupled to the controller means.
 19. The induction heating system ofclaim 16, wherein the first and second induction heating means compriseferrite core heating elements.
 20. The induction heating system of claim16, wherein the temperature sensing means comprise thermocoupletemperature sensors.
 21. The induction heating system of claim 16,wherein the temperature sensing means comprise pyrometer temperaturesensors.
 22. The induction heating system of claim 16, wherein thecontroller means provides a discernible indication when the workpieceshave reached the predetermined welding temperature.
 23. The inductionheating system of claim 22, wherein the discernible indication is avisual indication.
 24. The induction heating system of claim 16, whereinthe controller means provides positioning information to a positioningmeans that adjusts relative position of the tool until the predeterminedwelding temperature is achieved.
 25. The induction heating system ofclaim 16, wherein cooling fluid is provided proximate each of theheating means.
 26. The induction heating system of claim 25, wherein thecontroller means controls cooling fluid activation.
 27. The inductionheating system of claim 16, wherein there are three or more heatingmeans.
 28. The induction heating system of claim 16, wherein there arethree or more heating zones.
 29. The induction heating system of claim16, wherein the first and second workpieces are railroad rails.
 30. Amethod for preheating first and second workpieces to be welded together,the method comprising the steps of: (a) disposing, within a gap definedby facing ends of the workpieces, mounting means having first and secondopposing sides; (b) providing mechanical centering assemblies disposedadjacent the facing ends of the workpieces, wherein the mechanicalcentering assemblies position the mounting means longitudinally withrespect to the workpieces for proper proximity to the workpieces; (c)disposing a first induction heating means affixed to the first side ofthe mounting means proximate the first and second workpieces; (d)defining a first heating zone by positioning a first temperature sensingmeans proximate the first workpiece and the first heating means; (e)disposing a second induction heating means affixed to the second side ofthe mounting means proximate the first and second workpieces; (f)defining a second heating zone by positioning a second temperaturesensing means proximate the first workpiece and the second heatingmeans; and (g) activating the first and second heating meansindependently to achieve a predetermined welding temperature in bothfirst and second heating zones.